Root exudates of Withania somnifera prevent the risk of transmission of soil-dwelling Enterobacterales to nearby plants.

Soil-dwelling enteric pathogens are indicators of sewage or fecal matter contamination. When such organisms enter agricultural fields, they colonize crops and cause pre-harvest contamination of food products. Consumption of such contaminated products can lead to disease outbreaks. Thus, preventing pre-harvest contamination of food products by enteric bacteria dwelling in soil is essential. The Cooch Behar district of India receives > 3000 mm rainfall annually causing an anaerobic condition in soil, creating an ambient condition for the survival of enteric bacteria. While screening for native Enterobacterales in this region, a serendipitous observation was made, wherein the rhizosphere of Withania somnifera plant had negligible number of enteric bacteria. Artificially inoculated native Citrobacter sp. was unable to colonize the roots of Withania. Water-soluble exudates had prolonged antimicrobial activity in vitro, proving that the antimicrobial molecule is secretory. Based on this observation, Withania plant was grown in pots with high numbers of enteric bacteria, and it was found that the colonization was significantly reduced. Moreover, the antimicrobial activity spread through the soil via irrigation water to the neighboring plants. Thus, it was concluded that growing Withania alongside susceptible plants, like Vigna radiata, can prevent the colonization of the rhizosphere, minimizing the risk of pre-harvest contamination of fresh produce. Additionally, it was found that the antimicrobial activity is not specific. However, the population of beneficial microbiota of soil was not affected much when Vigna and Withania were grown together. To the best of our knowledge, this is the first report on Withania, as a biocontrol plant, that reduced the chance of spreading enteric bacteria in soil.